Influence of steric effect on the structural aspects of N,N′,N″-triarylguanidine derived six-membered [C,N] palladacycles

Article abstract of DOI:10.1016/j.poly.2012.06.077

Guanidine derived six-membered [C,N] palladacycles of the types [(C,N)Pd(μ-OC(O)R)]₂ (1a-d), [(C,N)Pd(μ-Br)]₂ (2a,b), cis-[(C,N)PdBr(L)] (3a-d, 4, and 5), and ring contracted guanidine derived five-membered [C,N] palladacycle, [(C,N)PdBr(CNXy)] (6) were prepared in high yield following the established methods with a view aimed at understanding the influence of the substituents on the aryl rings of the guanidine upon the solid state structure and solution behaviour of palladacycles. Palladacycles were characterised by microanalytical, IR, NMR and mass spectral data. The molecular structures of 1a, 1c, 2a, 2b, 3a, 3c, 3d, and 4-6 were determined by single crystal X-ray diffraction data. Palladacycles 1a and 1c were shown to exist as a dimer in transoid in-in conformation in the solid state but as a mixture of a dimer in major proportion and a monomer (κ²-O, O′-OAc) in solution as deduced from ¹H NMR data. Palladacycles 2a and 2b were shown to exist as a dimer in transoid conformation in the solid state but the former was shown to exist as a mixture of a dimer and presumably a trimer in solution as revealed by a variable temperature ¹H NMR data in conjunction with ESI-MS data. The cis configuration around the palladium atom in 3a, 3c, and 3d was ascribed to steric influence of the aryl moiety of NAr unit and that in 4-6 was ascribed to antisymbiosis. The solution behaviour of 3d was studied by a variable concentration (VC) ¹H NMR data.

Full text of DOI:10.1016/j.poly.2012.06.077

Polyhedron 52 (2013) 1041–1052
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Influence of steric effect on the structural aspects of N,N0,N00-triarylguanidine
derived six-membered [C,N] palladacycles
Kanniyappan Gopi a, Priya Saxena a, Munirathinam Nethaji b, Natesan Thirupathi a,
⇑
a Department of Chemistry, University of Delhi, Delhi 110 007, India
b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 6 July 2012
Guanidine derived six-membered [C,N] palladacycles of the types [(C,N)Pd(
l-OC(O)R)]2 (1a–d),
[(C,N)Pd( -Br)]2 (2a,b), cis-[(C,N)PdBr(L)] (3a–d, 4, and 5), and ring contracted guanidine derived five-
l
membered [C,N] palladacycle, [(C,N)PdBr(C„NXy)] (6) were prepared in high yield following the estab-
lished methods with a view aimed at understanding the influence of the substituents on the aryl rings
of the guanidine upon the solid state structure and solution behaviour of palladacycles. Palladacycles
were characterised by microanalytical, IR, NMR and mass spectral data. The molecular structures of 1a,
1c, 2a, 2b, 3a, 3c, 3d, and 4–6 were determined by single crystal X-ray diffraction data. Palladacycles
1a and 1c were shown to exist as a dimer in transoid in–in conformation in the solid state but as a mixture
of a dimer in major proportion and a monomer (j2-O,O0-OAc) in solution as deduced from 1H NMR data.
Palladacycles 2a and 2b were shown to exist as a dimer in transoid conformation in the solid state but the
former was shown to exist as a mixture of a dimer and presumably a trimer in solution as revealed by a
variable temperature 1H NMR data in conjunction with ESI-MS data. The cis configuration around the pal-
ladium atom in 3a, 3c, and 3d was ascribed to steric influence of the aryl moiety of @NAr unit and that in
4–6 was ascribed to antisymbiosis. The solution behaviour of 3d was studied by a variable concentration
(VC) 1H NMR data.
This article is dedicated to 100th
anniversary celebration of the award of
Nobel Prize in chemistry to Professor Alfred
Werner.
Keywords:
Guanidine
Palladacycle
Conformer
Lewis base
n–p conjugation
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
guanidinium salt [(ArNH)3C]+Xꢀ upon protonation under facile
condition. This feature of N,N0,N00-triarylguanidines in conjunction
The imine derived six-membered [C,N] palladacycles are one of
the interesting classes of palladacycles due their relevance as pre-
catalysts in C–C and C–heteroatom bond forming reactions [1–4],
their intriguing structural and reactivity pattern including regiose-
lective aspects of C–H activation process [5–11], and as scaffolds
that exhibit interesting photophysical properties [12,13]. Further,
the six-membered ‘‘[C,N]Pd’’ skeleton is often encountered as a
reactive intermediate in palladium mediated organic transforma-
tions [14,15].
with the ready tunability of the aryl moieties were anticipated to
facilitate cyclopalladation reaction upon treatment with palla-
dium(II) carboxylates. We have recently reported the synthesis,
reactivity studies, structural aspects, and solution dynamics of
(ArNH)2C@NAr (Ar = 2-(MeO)C6H4; LH22-anisyl) derived six-mem-
bered and ring contracted five-membered [C,N] palladacycles
2-anisyl
[18]. In these palladacycles, LH2
was shown to act as mono-
anionic [C,N] donor ligand (j2C,N) to the palladium (Chart 1). We
want to address how the sterically more hindered aryl moieties in
2-tolyl
Sym N,N0,N00-trisubstituted guanidines, RN@C(NHR)2 (R = alkyl,
and aryl) are one of the interesting classes of nitrogen donor li-
gands as they have the ability to coordinate to the metal ions
(ArNH)2C@NAr (Ar = 2-MeC6H4 (LH2
)
and 2,4-Me2C6H3
and their conforma-
2-anisyl
(LH22,4-xylyl)) than those present in LH2
tional difference (anti–anti
aba versus syn–anti abb) [19] influ-
(j (
1N), chelating monoanionic j2N,N0),
ence the solid state structures and solution behaviour of LH2
2-tolyl
in their neutral form
bridging monoanionic
j1N;j1N0), and chelating dianionic
and LH2
derived [C,N] palldacycles. Towards these goals,
2,4-xylyl
(l2-
forms (j2N,N0) as illustrated in Chart 1 [16,17]. Sym N,N0,N00-tria-
rylguanidines, ArN=C(NHAr)2 are more basic than the correspond-
ing arylimines due to the ability of the former to form the
we describe herein the synthesis, structural aspects and solution
2-tolyl
2,4-xylyl
behaviour of LH2
and LH2
derived six-membered
2-tolyl
[C,N] palladacycles (1a–d, 2a–b, 3a–d, 4 and 5) and LH2
derived ring contracted five-membered [C,N] palladacycle, (6)
and compare the structural features of these palladacycles with
⇑
Corresponding author.
2-anisyl
the corresponding palladacycles derived from LH2
.
E-mail
addresses:
tnat@chemistry.du.ac.in,
thirupathi_n@yahoo.com
(N. Thirupathi).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.06.077

1042
K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
and the analogous reaction carried out with Pd(TFA)2 (TFA:
2. Results and discussion
OC(O)CF3) in toluene at 58 °C afforded 1b in 81% yield. The reaction
of LH22,4-xylyl with Pd(OAc)2 and Pd(TFA)2 carried out separately in
toluene at 58 °C for 8 h afforded 1c and 1d, respectively in 88%
yield (Scheme 1).
2.1. The carboxylato bridged [C,N] palladacycles (1a–1d)
LH22-tolyl was treated with Pd(OAc)2 in toluene at 70 °C for 8 h to
afford 1a in 91% yield following the C–H activation process [20–22]
The molecular structures 1a, and 1c have been determined by
single crystal X-ray diffraction data and are depicted in Fig. 1. Se-
lected bond distances and bond angles are listed in Table 1. The
palladium atom is surrounded by four atoms – imine nitrogen, aryl
carbon, and one oxygen atom from each of the two syn–syn biden-
tate bridging acetate moiety and thus possesses a slightly distorted
square planar geometry. Palladacycles 1a and 1c possess a crystal-
lographic C2 symmetry and a pseudo C2 symmetry, respectively
that passes vertically across the Pdꢁ ꢁ ꢁPd non-bonded axis and this
arrangement affords a transoid in–in conformation. In transoid
form, the imine nitrogen or metalated carbon of one six-membered
‘‘[C,N]Pd’’ ring is placed opposite to the identical atom in the other
half of the palladacycle whereas in the cisoid form these atoms are
placed on the same side. The in–in, in–out and out–out nomencla-
ture refers to the orientation of the NH proton of one six-mem-
bered ‘‘[C,N]Pd’’ ring with respect to the orientation of the NH
proton of the remaining six-membered ‘‘[C,N]Pd’’ ring.
R
R
N
H
H
N
H
R
N
N
N
R
R
R
R
R
R
N
N
N
H
N
M
M
M
M
Monodentate
Chelating Monoanionic Bidentate Bridging
κ1N
κ2N,N′
Monoanionic
μ2−κ1N:κ1N′
R
H
N
H
N
N
R
R
Ar
N
N
R
N
M
Ar
M
The six-membered ‘‘[C,N]Pd’’ ring in 1a and 1c adopts a pseudo
boat conformation wherein the Pd atom and the endocyclic NH
nitrogen atom occupy the tips of the boat while the remaining
atoms occupy the basal plane of the boat. The o-Me substituent
Chelating Dianionic
Chelating Monoanionic
κ2N,N′
κ2C,N
Chart 1.
Ar
ArHN
Ar
N
OC(O)R′
N
HN
Pd
Toluene
8 h
H
Ar
Pd(O(CO)R')2
+
N
H
N
2
Me
Ar
R
2-tolyl
′
Ar = 2-MeC6H4 (LH2
)
Ar
R
H
H
Me
Me
R
2,4-xylyl
Ar = 2,4-Me2C6H3 (LH2
)
1a
1b
2-MeC6H4
2-MeC6H4
1c 2,4-Me2C6H3
1d 2,4-Me2C6H3
Me
CF3
Me
CF3
Scheme 1. Temperature: 70 °C (1a); 58 °C (1b–1d).
Fig. 1. Molecular structures of 1a and 1c at the 30% probability level. Two molecules crystallised in an asymmetric unit but only molecule 1 of 1c is shown for clarity.
Hydrogen atoms except amino hydrogens and toluene in the case of 1a are omitted for clarity.

K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
1043
Table 1
R
N
Selected bond distances (Å) and bond angles (°) for 1a and 1c.
1a
Me
Me
Pd1–N1
Pd1–C19
Pd1–O1
Pd1–O2
C10–N1
C10–N2
C10–N3
2.022(2)
1.964(3)
2.134(2)
2.066(2)
1.311(4)
1.363(4)
1.346(4)
Pd1ꢁ ꢁ ꢁPd1
2.9326(7)
90.95(7)
87.24(8)
91.61(9)
90.1(1)
H
N
N1–Pd1–O1
O1–Pd1–O2
C19–Pd1–O2
C19–Pd1–N1
N1–Pd1–O2
C19–Pd1–O1
Me
R
O
HN
Pd
R
Me
177.67(7)
174.55(9)
O
1c (molecule 1)
Pd1–N1
Pd1–C23
Pd1–O1
Pd1–O3
C13–N1
2.013(5)
1.966(6)
2.129(4)
2.041(4)
1.282(7)
1.382(7)
1.346(8)
Pd2–N4
Pd2–C48
Pd2–O2
Pd2–O4
C38–N4
C38–N5
C38–N6
Pd1ꢁ ꢁ ꢁPd2
C48–Pd2–O2
N4–Pd2–O4
O2–Pd2–O4
N4–Pd2–O2
C48–Pd2–O4
C48–Pd2–N4
2.004(4)
1.953(6)
2.050(4)
2.153(4)
1.301(6)
1.361(7)
1.368(7)
2.983(2)
90.3(2)
92.8(2)
88.0(2)
177.7(2)
172.4(2)
88.6(2)
R = H (A), Me (B)
C13–N2
C13–N3
Chart 2.
O3–Pd1–O1
N1–Pd1–O3
N1–Pd1–O1
C23–Pd1–O1
C23–Pd1–O3
C23–Pd1–N1
86.7(2)
175.4(2)
91.4(2)
173.5(2)
90.9(2)
90.6(2)
Table 2
Population of species 1 and 2 of 1c as a function of concentration as estimated by 1
NMR (400 MHz, CDCl3) data. The CH3 signals at d = 1.82 and 1.95 ppm were used as
H
reference peaks to estimate the population of species 1 and species 2, respectively.
Conc. (mM)
5.0
7.8
21.8
38.7
Species 1
Species 2
1.00
0.40
1.00
0.23
1.00
0.10
1.00
0.08
of the @NAr unit orients downward from the basal plane of the
boat (i.e. b conformation) as analogously observed in [Pd{
2(C,N)-
C6H3(OMe)-3(NHC(NHAr)(@NAr))-2}( -OAc)]2 (Ar = 2-(MeO)C6H4;
I) [18]. The non-bonded Pdꢁ ꢁ ꢁPd distance, 2.9326(7) Å in 1a is com-
parable with that known for [Pd{
2(C,N)-C6H4(NHC(Ph)(@NPh))-
2}( -OAc)]2 (2.9435(4) Å) [23] but is shorter than that known for
I (3.005(2) Å) [18], and 1c (2.983(2) Å; molecule 1). This trend
arises possibly due to the lesser electron richness of the palladium
atom in 1a caused by less strongly donating guanidine unit than
the more electron richness of the palladium atom in I [18] and
1c caused by more strongly donating guanidine units.
The Pd–O bond trans to the aryl carbon is longer than the Pd–O
bond that is trans to the imine nitrogen in 1a (2.134(2), 2.066(2) Å)
and 1c (2.129(4), 2.041(4); 2.153(4), 2.050(4) Å (molecule 1)) due
to greater trans influence of the aryl carbon. The bond length differ-
ence between the C@N double bond and the adjacent endocyclic
C–N(H) single bond (DCN = d(C–N) ꢀ d(C@N)) or the adjacent exo-
cyclic C–N(H) single bond (D0CN = d(C–N) ꢀ d(C@N)) have been used
j
l
revealed concentration dependent 1H NMR spectral pattern (Ta-
ble 2). Thus, from the results of VT and variable concentration
(VC) 1H NMR studies, we suggest that species 1 corresponds to
the dimer 1c and species 2 corresponds to the monomer B
(Chart 2).
j
l
In solution, some [C,N] palladacycles were shown to undergo
the acetato ring inversion [25] or the six-membered ‘‘[C,N]Pd’’ ring
inversion [26,27] or the latter process in conjunction with the ace-
tato cleavage process to afford transoid in–in, transoid in–out, and
transoid out–out conformers as well as monomeric pincer type
and j2-O,O0-OAc palladacycles as established for I [18]. The differ-
ence in solution behaviour between 1a and 1c on the one hand and
that of I [18] on the other is ascribed to higher steric bulk of o-Me
group of @NAr unit in the former palladacycles compared with o-
OMe group of the same unit in the latter. Further, the ability of
o-OMe group of @NAr unit in I to participate in anchimeric assis-
tance is believed to be responsible for the formation of monomeric
pincer-type palladacycle in solution. Interestingly, the 1H NMR
spectrum of 1b and 1d revealed the presence of only one isomer
in solution at ambient condition that contrasts with the 1H NMR
pattern of 1a and 1c. This could be probably ascribed to the greater
reactivity of 1a and 1c towards solvents in bridge-splitting reaction
to afford A and B, respectively as compared to their trifluoroacetato
analogues, 1b and 1d.
to understand the degree of n–
p conjugation involving the N(H)
lone pair with the C@N p⁄ orbital of the imine unit [18,19,24].
DCN: 0.035(6) Å value in 1a is smaller than D0CN: 0.052(6) Å value
indicating a more favourable alignment of the lone pair on the
endocyclic amino nitrogen with the C@N p⁄ orbital than that on
the exocyclic amino nitrogen. Further, DCN and D0CN values of 1a
are smaller than that known for LH2
2-tolyl
( :
DCN: 0.095(6) and DC0 N
0.098(6) Å) [19] indicating an improved n–
ladacycle formation. The DCN: 0.064(11) Å value is smaller but DC0 N
0.100(10) Å value is comparable for the guanidine moiety bound to
p conjugation upon pal-
:
2,4-xylyl
Pd1 in 1c relative to that known for LH2
(DCN: 0.091(3) Å and
2.2. The bromo bridged [C,N] palladacycles (2a and 2b)
D0CN: 0.108(3) Å) [19] perhaps due to subtle packing forces in the
crystal lattice. The amino nitrogens in 1a and 1c are planar or
nearly planar.
Palladacycles 1a and 1c upon metathetical reaction with excess
of LiBr in aqueous ethanol at 78 °C for 8 h afforded 2a and 2b in
87% and 85% yield, respectively (Scheme 2). The molecular struc-
tures of 2a and 2b have been determined by single crystal X-ray
diffraction data and are depicted in Fig. 2. Selected bond distances
and bond angles are listed in Table 3.
The imine derived halo bridged six-membered [C,N] palladacy-
cles are known to exist as transoid [4,28–31] and cisoid [15,32] con-
formers. Palladacycles 2a and 2b exist as a dimer in transoid form
and the former possesses a crystallographic C2 symmetry that
A variable temperature (VT) 1H NMR data of 1a indicated the
presence of two species with one of them being predominant at
ambient temperature. However, only one species was observed
at temperatures 6253 K (Fig. S1 in the Supplementary data). The
major species in solution was assigned to the acetate bridged di-
mer, 1a and the minor species was assigned to the j2-O,O0-OAc
monomer A, illustrated in Chart 2. The 1H NMR spectrum of 1a
at 5.0 mM concentration revealed two species in about 1.00:0.15
ratio but only one species was observed at 101.2 mM concentra-
tion as revealed by 1H and 13C NMR data. Palladacycle 1c also
passes vertically across the centre of the puckered [Pd(
unit while the latter does not possess such symmetry. The six-
l
-Br)2Pd]2+

1044
K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
II) [18] can be explained by invoking a greater steric bulk of the o-
Ar
Ar
ArHN
HN
ArHN
HN
Me substituent of @NAr unit in the former palladacycles than o-
OMe substituent of the same unit in the latter. The dihedral angle
between two PdBr2 planes in 2a (/: 21.77(2)°) is much smaller than
that observed in 2b (/: 54.94(2)°) and as a result, the non-bonded
Pdꢁ ꢁ ꢁPd distance, 3.6635(9) Å in the former is greater than the corre-
sponding distance, 3.3804(4) Å observed in the latter. Two types of
Pd–Br distances (2.4439(7), 2.5853(8) Å (2a), 2.4501(5), 2.5840(5) Å
(2b)) are typical for [C,N] palladacycles.
Br
OC(O)Me
N
N
(i)
Pd
Pd
2
2
Me
Me
R
R
Palladacycle 2a was subjected to a VT 1H NMR study to under-
stand its solution behaviour. The stack plot for CH3 protons of the
guanidine moiety is shown in Fig. 3. At 298 K, three peaks were ob-
served at d = 1.63, 2.07 and 2.34 ppm assignable to CH3 protons of
the guanidine moiety and these peaks decoalesce into six peaks
(d = 1.61, 1.62, 2.03, 2.04, 2.30 and 2.31 ppm) at 268 K. The 1H
NMR pattern remains almost unaltered below 268 K. The ESI-MS
mass spectrum of 2a revealed peaks at m/z = 1464, 949 and
475 amu assignable to [trimerꢀBr]+, [2aꢀBr]+ and [(C,N)Pd+K]+
fragments, respectively (Fig. S2 in the Supplementary data). The
ESI-MS mass spectrum of 2b revealed peaks at m/z = 1592 and
1122 assignable to the [trimerꢀBr]+ and [2b+Li]+, respectively. It
is to be noted that the number of 13C NMR signals for the aryl car-
bons of 2b is greater than expected, possibly due to the presence of
R
H
Me
Ar
2-MeC6H4
2,4-Me2C6H3
1a
1c
2a
2b
Scheme 2. (i) LiBr, EtOH–H2O (9:1), 78 °C, 8 h.
membered ‘‘[C,N]Pd’’ ring of two halves of the molecule and the
four-membered [Pd(
-Br)2Pd]2+ ring are puckered in the same
direction in 2a (i.e. butterfly like framework) but these rings are
l
puckered in opposite direction in 2b (i.e. bat like framework). The
puckered conformation of the [Pd(
sus a planar rhomboid conformation of the same unit in [Pd{
C6H3(OMe)-3(NHC(NHAr)(@NAr))-2}( -Br)]2 (Ar = 2-(MeO)C6H4;
l
-Br)2Pd]2+ ring in 2a and 2b ver-
j
2(C,N)-
l
Fig. 2. Molecular structures of 2a and 2b at the 30% probability level. Hydrogen atoms except amino hydrogens and solvent molecules are omitted for clarity.

K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
1045
Table 3
Me
H
N
Selected bond distances (Å) and bond angles (°) for 2a and 2b.
NHAr
Ar
2a
R
Pd1–N1
Pd1–C17
Pd1–Br1
Pd1–Br1
C1–N1
2.036(4)
1.971(5)
2.4439(7)
2.5853(8)
1.301(7)
1.365(7)
1.346(7)
3.6635(9)
N1–Pd1–Br1
C17–Pd1–N1
C17–Pd1–Br1
C17–Pd1–Br1
Br1–Pd1–Br1
Pd1–Br1–Pd1
C1–N1–Pd1
C1–N3–C16
96.2(1)
88.0(2)
91.5(2)
175.8(2)
84.28(2)
93.47(2)
122.0(3)
124.5(5)
N
R
Pd
Ar
Br
Br
ArHN
N
Pd
Pd
N
Me
C1–N2
C1–N3
Br
Ar
NH
HN
Me
Pd1ꢁ ꢁ ꢁPd1
N1–Pd1–Br1
173.3(1)
NHAr
R
2b
Pd1–C19
Pd1–N1
Pd1–Br1
Pd1–Br2
N1–C1
1.979(4)
2.037(3)
2.4501(5)
2.5840(5)
1.298(5)
1.353(5)
1.354(5)
2.039(3)
1.988(4)
2.5961(5)
2.4552(6)
1.293(5)
1.372(5)
1.353(5)
3.3804(4)
C19–Pd1–N1
C19–Pd1–Br1
C19–Pd1–Br2
N1–Pd1–Br1
Br2–Pd1–Br1
N1–Pd1–Br2
Pd2–Br1–Pd1
Pd1–Br2–Pd2
C44–Pd2–N4
C44–Pd2–Br1
N4–Pd2–Br2
Br1–Pd2–Br2
N4–Pd2–Br1
C44–Pd2–Br2
88.6(2)
93.9(1)
172.8(1)
173.2(1)
82.12(2)
96.02(9)
84.06(2)
84.22(2)
89.0(2)
173.1(1)
173.9(1)
81.77(2)
95.28(9)
94.5(1)
Ar
R
H
C
D
2-MeC6H4
2,4-Me2C6H3
Me
N2–C1
N3–C1
Chart 3.
Pd2–N4
Pd2–C44
Pd2–Br1
Pd2–Br2
N4–C26
N5–C26
N6–C26
Pd1ꢁ ꢁ ꢁPd2
2.3. Monomeric [C,N] palladacycles (3a–d, 4, 5 and 6)
A suspension of 2a in CH2Cl2 was treated with 2,6-lutidine,
3,5-lutidine, 2,4-lutidine, tBuN„C and PTA (1,3,5-triaza-7-phos-
phatricyclo[3.3.1.1]decane) in 1:1 (Pd:L) mole ratio at ambient
temperature to afford 3a–3c, 4, and 5, respectively in 83–88%
yield. Similarly, 2b was treated with 2,6-lutidine in 1:1 (Pd:L)
mole ratio in CH2Cl2 at ambient temperature to afford 3d in
93% yield (Scheme 3, step i). Palladacycle 2a was treated
with XyN„C in 1:1 (Pd:L) mole ratio in CH2Cl2 at ambient tem-
perature to afford [Pd{j
2(C,N)-C6H3Me-3(NHC(NHAr)(@NAr))-
2}Br(C„NXy)] (Ar = 2-MeC6H4; Xy = 2,6-Me2C6H3) but this at-
tempt proved futile and the starting materials remained largely
t
unreacted. The difference in reactivity pattern between BuN„C
and XyN„C toward 2a could be attributed to the higher nucleo-
philicity of the former [33] that enables cleavage of 2a to afford 4.
The insertion reaction of 2a with XyN„C carried out in 1:2 (Pd:L)
mole ratio in CH2Cl2 at ambient condition for 24 h led to the for-
mation of a ring contracted five-membered [C,N] palladacycle, 6
in 93% yield. This reaction appears to proceed through a seven-
membered [(C,N)PdBr(C„NXy)] intermediate that upon ring con-
traction followed by amine–imine tautomerisation afforded 6 as
previously proposed in the formation of [Pd{
C(@NXy)(C6H3(OMe)-4)-2(N@C(NHAr)2)-3}Br(C„NXy)]
(MeO)C6H4; III) [18] (Scheme 3, step ii).
j
2(C,N)-
(Ar = 2-
The molecular structures of 3a, 3c, 3d, 4–6 have been deter-
mined by single crystal X-ray diffraction data and are depicted in
Fig. 4. Selected bond distances and bond angles are listed in Tables
4–6. The palladium atom in these palladacycles revealed a some-
what distorted square planar geometry. The Lewis base is coordi-
nated to the palladium atom in cis relation with respect to the
Pd–C bond. The molecular structures of imine derived six-mem-
bered [C,N] palladacycles of the type [(C,N)PdX(L)] (L = pyridine,
and
phosphine
[4,34–38]),
and
[Pd{j
2(C,N)-C6H3(OMe)-
3(NHC(NHAr)(@NAr))-2}Br(C„NXy)] (Ar = 2-(MeO)C6H4; IV [18])
are known to contain the Lewis base cis to the Pd–C bond due
to antisymbiosis. However, an unusual trans configuration was
observed for the palladium atom in [Pd{j
2(C,N)-C6H3(OMe)-
3(NHC(NHAr)(@NAr))-2}Br(L)] (Ar = 2-(MeO)C6H4; L = 2,6-
Me2C5H3N (Va), 2,4-Me2C5H3N (Vb)) [18] and such configuration
was explained by invoking relative hardness/softness of the donor
atoms surrounding the palladium and its antisymbiotic behaviour
[39]. The greater steric bulk of the aryl moiety of the @NAr unit in
3a, 3c, and 3d than that present in Va and Vb could be the reason
for the reversal of stereochemistry around the palladium atom
rather than antisymbiosis. There would be an unfavourable steric
Fig. 3. A VT 1H NMR (400 MHz, CD2Cl2) spectrum of 2a shown for CH3 protons of
the guanidine moiety. The d symbol indicates proton signal of adventitious H2O.
two species in solution. From the results of NMR and mass spectral
data, we conclude that 2a and 2b exist as dimer in the solid state
but as a mixture of a dimer and presumably a trimer (C and D)
in solution (Chart 3).

1046
K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
Ar
ArHN
HN
Br
L
N
(i)
Pd
Bridge-splitting
reaction
Me
R
Ar
R
H
H
H
L
Ar
ArHN
HN
3a
3b
3c
2-MeC6H4
2-MeC6H4
2-MeC6H4
2,6-Me2C5H3N
3,5-Me2C5H3N
2,4-Me2C5H3N
Br
N
CH2Cl2
Pd
RT, 24 h
2
3d 2,4-Me2C6H3 Me 2,6-Me2C5H3N
tBuN≡C
PTA
Me
4
5
2-MeC6H4
2-MeC6H4
H
H
R
NHAr
Br
ArHN
Me
Ar
2-MeC6H4
2b 2,4-Me2C6H3 Me
R
H
2a
N
N
(ii)
Insertion reaction
Pd
C≡NXy
Xy
6
Ar = 2-MeC6H4
Xy = 2,6-Me2C6H3
Scheme 3. (i) Pd:L (1:1); (ii) Pd:C„NXy(1:2).
Fig. 4. Molecular structures of 3a, 3c, 3d, and 4–6 at the 30% probability level. Hydrogen atoms except amino hydogens and methanol in the case of 5 are omitted for clarity.
repulsion between the o-Me group of lutidine and that of the @NAr
moiety in a hypothetical trans isomer of 3a, 3c, and 3d and hence
cis configuration is preferred. The cis configuration of the palladium
atom in 4 and 5 could be ascribed largely to antisymbiosis, as anal-
ogously suggested for IV [18]. The Lewis base in 4, and 5 could be
softer than bromine and hence prefers to lie trans to the harder
imine nitrogen atom.
The Pd–Br distance is longer while the Pd–N(lutidine) distance
is shorter in 3a (Pd–Br: 2.5491(2) Å; Pd–N: 2.048(1) Å), 3c (Pd–Br:
2.5601(5) Å; Pd–N: 2.048(3) Å), and 3d (Pd–Br: 2.535(1) Å; Pd–N:
2.035(6) Å) than those observed in Va (Pd–Br: 2.441(6) Å;
Pd–N: 2.173(4) Å (molecule 1)) and Vb (Pd–Br: 2.446(5) Å; Pd–N:
2.160(3) Å) [18] as the bromine atom is trans to the softer aryl car-
bon in the former set of palladacycles. The six-membered ‘‘[C,N]Pd’’

K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
1047
Table 4
Table 7
Selected bond distances (Å) and bond angles (deg) for 3a, 3c, and 3d.
Population of two isomers of 3d as a function of concentration as estimated by 1H
NMR (400 MHz, CDCl3) data. The CH3 signals of 2,6-lutidine at d = 2.67 and 2.97 ppm
were used as reference peaks to estimate the population of isomer 2 and isomer 1,
respectively.
3a
Pd1–N1
Pd1–C17
Pd1–N4
Pd1–Br1
N1–C1
2.034(1)
1.985(2)
2.048(1)
2.5491(2)
1.311(2)
1.361(2)
C17–Pd1–N1
C17–Pd1–N4
N1–Pd1–Br1
N4–Pd1–Br1
N1–Pd1–N4
C17–Pd1–Br1
88.53(6)
91.03(6)
95.03(4)
85.50(4)
178.92(5)
173.51(5)
Conc. (mM)
6.4
32.2
58.0
83.9
109.7
364.0
Isomer 1
Isomer 2
1.00
0.08
1.00
0.11
1.00
0.12
1.00
0.13
1.00
0.14
1.00
0.28
N2–C1
3c
Pd1–N1
Pd1–C17
Pd1–N4
Pd1–Br1
N1–C1
N2–C1
N3–C1
2.039(3)
1.997(4)
2.048(3)
2.5601(5)
1.308(5)
1.356(5)
1.343(5)
C17–Pd1–N1
C17–Pd1–N4
N1–Pd1–Br1
N4–Pd1–Br1
N1–Pd1–N4
C17–Pd1–Br1
89.7(2)
92.4(2)
94.38(9)
83.54(9)
177.5(1)
175.6(1)
conformation for the six-membered ‘‘[C,N]Pd’’ ring in solution too
as previously shown for Va [18] and the related palladacycles
[25]. The CH3 protons of 3,5-lutidine in 3b are isochronous as these
protons are placed farther away from the centre of the boat.
A variable temperature 1H NMR study carried out on the sample
of 3d did not indicate any spectral change throughout the temper-
ature range studied. (Figs. S3 and S4 in the Supplementary data).
Presumably, the six-membered ‘‘[C,N]Pd’’ ring inversion occurs fas-
ter than the NMR timescale due to the presence of sterically more
hindered @NAr unit. Palladacycle 3d was subjected to a VC 1H NMR
study and the results are listed in Table 7. The population of isomer
2 increases although not smoothly upon increasing the concentra-
tion of the analyte. The population of the isomer at a particular
concentration appears to depend upon the subtle balance between
the steric effect and noncovalent interactions. It may be that non-
covalent interactions such as intermolecular N–Hꢁ ꢁ ꢁBr and C–
Hꢁ ꢁ ꢁBr hydrogen bonding is predominant over steric effect in the
solid-state to afford the isomer 2 (i.e. b conformer) but such inter-
actions play no significant role in dilute solution and hence the
population of solution conformer is solely determined by steric fac-
tor (Fig. S5 in the Supporting Information). The role of noncovalent
interactions becomes increasingly important upon increasing the
concentration of the analyte as the molecules approach close to
one another and hence the population of isomer 2 increases rela-
tive to isomer 1. The isomer 2 could be a kinetic rather than a ther-
modynamic product of the crystallisation process [40]. Based on
3d
Pd1–N1
Pd1–C19
Pd1–N4
Pd1–Br1
N1–C1
N2–C1
N3–C1
2.037(6)
2.046(8)
2.035(6)
2.535(1)
1.29(1)
1.38(1)
1.37(1)
N1–Pd1–C19
N1–Pd1–Br1
N4–Pd1–C19
N4–Pd1–Br1
N4–Pd1–N1
C19–Pd1–Br1
89.0(3)
93.7(2)
91.1(3)
86.2(2)
179.0(3)
175.0(2)
Table 5
Selected bond distances (Å) and bond angles (°) for 4 and 5.
4
Pd1–N1
Pd1–C17
Pd1–C23
Pd1–Br1
N1–C1
N2–C1
N3–C1
N4–C23
2.049(3)
2.004(3)
1.933(4)
2.5273(5)
1.294(4)
1.372(4)
1.357(4)
1.136(5)
C17–Pd1–N1
C23–Pd1–C17
C23–Pd1–Br1
N1–Pd1–Br1
C23–Pd1–N1
C17–Pd1–Br1
N4–C23–Pd1
89.1(1)
89.6(2)
85.2(1)
96.09(7)
175.2(1)
174.8(1)
177.7(4)
5
Pd1–N1
Pd1–C17
Pd1–P1
Pd1–Br1
N1–C1
N2–C1
N3–C1
2.111(4)
2.007(5)
2.247(1)
2.522(1)
1.313(7)
1.357(6)
1.363(7)
C17–Pd1–N1
C17–Pd1–P1
N1–Pd1–Br1
P1–Pd1–Br1
N1–Pd1–P1
C17–Pd1–Br1
88.1(2)
93.2(1)
94.2(1)
85.45(4)
166.1(1)
175.6(1)
the VC 1H NMR results, we assign isomer 1 to the
and the isomer 2 to the b conformer in solution. and b conform-
a conformer
a
ers of 3a, 3b and 3d differ from each other in the orientation of
o-Me group of the @NAr unit with respect to the basal plane of
the boat (Scheme 4).
The 1H NMR spectrum of 3c revealed the presence of four iso-
mers in about 3.0:2.3:0.5:0.5 ratios as estimated from the 1H
NMR integrals of CH3 protons of 2,4-lutidine. One pair of isomers
Table 6
Selected bond distances (Å) and bond angles (°) for 6.
is assigned to
to a0 and b0 conformers.
a six-membered ‘‘[C,N]Pd’’ ring inversion as do a0 and b0 conform-
ers.
and a0 conformers and b and b0 conformers interconvert via
a
and b conformers and the other pair is assigned
a
and b conformers can interconvert via
Pd1–N1
2.090(2)
2.011(3)
2.5980(3)
1.944(3)
1.318(3)
1.363(3)
1.353(3)
1.259(4)
1.150(3)
81.11(9)
96.73(5)
C32–Pd1–C23
C32–Pd1–Br1
C32–Pd1–N1
C23–Pd1–Br1
C1–N1–C16
C1–N1–Pd1
C16–N1–Pd1
C23–N4–C24
N5–C32–Pd1
C32–N5–C33
97.7(1)
84.99(8)
177.0(1)
168.69(9)
123.5(2)
123.4(2)
108.8(2)
125.4(3)
166.7(2)
173.0(3)
Pd1–C23
Pd1–Br1
Pd1–C32
N1–C1
N3–C1
N2–C1
N4–C23
N5–C32
C23–Pd1–N1
N1–Pd1–Br1
a
the Pd–N(lutidine) bond rotation or dissociation followed by reco-
ordination of lutidine. Ryabov and co-worker have shown that the
second pathway is unlikely for the related six-membered [C,N] pal-
ladacycle [41], although such pathway is usually proposed to ex-
plain the formation of two isomers of five-membered [C,N]
palladacycles of the type [(C,N)PdCl(L)] [42,43]. Thus, we suggest
that
Pd–N(lutidine) bond rotation.
Unlike Va and Vb, and b conformers of 3a, 3b and 3d can also
a M
a0 or b M b0 interconversion possibly occurs through the
a
interconvert via @N–C(Ar) single bond rotation [44,45] but this
ring in 3a, 3d, 4 and 5 revealed a pseudo boat b conformation that
contrasts with the pseudo boat conformation observed for the
same ring in IV, Va and Vb. The structural features of 6 are identical
process is unlikely in the latter palladacycles due to steric factor.
a
However,
a
and b conformers and a0 and b0 conformers can inter-
convert through a planar intermediate via the six-membered
‘‘[C,N]Pd’’ ring inversion as discussed for Va [18]. The effective ste-
ric bulk of o-Me substituent of @NAr moiety in 3a–3d is greater
than that of o-OMe substituent of the same unit in Va, and Vb
and hence the former palladacycles are less stable in the planar
conformation than the latter.
with those found in III [18].
The 1H NMR spectrum of 3a, 3b and 3d revealed the presence of
two isomers in about 3.0:1.0, 3.0:1.5 and 3.0:0.6 ratio, respectively
as estimated from the intensities of CH3 protons of lutidine and
those of the guanidine moiety. Further, 3a and 3d revealed two sig-
nals for CH3 protons of 2,6-lutidine that indicates a pseudo boat

1048
K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
NMR data were acquired on Jeol ECX 400 NMR spectrometer oper-
R1
R4
R3
R2
ating at 400, 100.81 MHz, respectively. The 13C NMR assignments
of 1a, 2b, and 4 were made with the aid of DEPT and HETCOR
NMR data (Figs. S6–S14 in the Supplementary data). The 31P
NMR data of 5 was recorded on Jeol ECX 400 NMR spectrometer
operating at 161.8 MHz with 85% H3PO4 as the external standard.
The experimental procedures for 1a–1d are analogous to that de-
scribed previously for I, those of 2a and 2b are analogous to that
described previously for II, those of 3a–3d are analogous to that
described previously for Va while that of 6 is analogous to that de-
scribed previously for III [18].
′
Me
N
R3
ArHN
N
′
N
R2
Br
H
(i)
N
Pd
Pd
Br
H
R2
N
N
Me
′
R2
ArHN
R3
′
R3
R1
R4
α
β
4.2. Synthesis, analytical and spectroscopic data of [C,N] palladacycles
(ii)
R4
(ii)
4.2.1. Palladacycle 1a
Yield:
Pd2C48H50N6O4ꢁC7H8 (Mw: 1079.95): C, 61.17; H, 5.41; N, 7.78.
Found: C, 60.86; H, 5.42; N, 7.62%. IR (KBr, cmꢀ1):
(NH) 3426 m,
3397 m; (C@N) 1629 vs; a(OCO) 1575 vs,
s(OCO) 1404 s. 1H
91%.
Mp(DSC):
196.30 °C.
Anal.
Calc.
for
R1
′
R3
Me
N
R3
m
ArHN
N
m
m
m
′
R2
R2
Br
N
NMR (400 MHz, CDCl3, 5.0 mM): dimer, 1a: monomer,
A ꢂ 1.00:0.15; d 1.37 (s, 6H, CH3, 1a), 1.69 (s, 6H, CH3, 1a), 1.76
(s, 3H, CH3, A), 1.86 (s, 6H, CH3, 1a), 1.94, 2.21 (each s, 2 ꢃ 3H,
CH3, A), 2.53 (s, 6H, CH3, 1a), 2.55 (s, 3H, CH3, A), 5.36 (s, 3H,
NH), 6.09 (s, 3H, NH), 6.47 (dd, JHH = 7.8; 2.0 Hz, 3H, ArH), 6.82,
6.83 (br, 3H, ArH), 6.91–6.93 (m, 6H, ArH), 6.99–7.03 (m, 6H,
ArH), 7.10–7.23 (m, 12H, ArH), 7.65–7.67 (m, 3H, ArH). 1H NMR
(300 MHz, CDCl3, 101.2 mM): dimer, 1a; d 1.37 (s, 6H, CH3), 1.69,
1.85, 2.53 (each s, 6 ꢃ 3H, CH3), 5.35 (s, 2H, NH), 6.09 (s, 2H, NH),
6.49 (br, 2H, ArH), 6.82 (br, 2H, ArH), 6.92 (br, 2H, ArH), 7.02 (br,
2H, ArH), 7.16 (br, 12H, ArH), 7.68 (br, 2H, ArH). 13C NMR
(100.81 MHz, CDCl3, 101.2 mM): dimer, 1a; d 17.5, 19.3, 23.7
(CH3), 119.0 (C), 120.5 (CH), 121.6 (C), 125.8 (CH), 126.2 (CH),
127.2 (CH), 127.3 (CH), 128.1 (CH), 131.4 (CH), 131.5 (CH), 134.3
(C), 134.4 (CH), 134.6 (C), 135.3 (C), 143.6 (C), 144.0 (C), 179.6
(OC(O)). Note: Only three carbon peaks were observed for CH3 car-
bon rather than the expected four peaks due to overlap at
d = 17.5 ppm and only 16 carbon resonances were observed for
ArC and C@N carbons rather than the expected 19 peaks, presum-
ably due to overlapping peaks. TOF MS+, m/z (relative intensity%),
H
(i)
N
Pd
N
Pd
Br
′
H
R2
N
Me
R2
R3
β′
ArHN
′
R3
R4
R1
α′
Scheme 4. Conformational equilibria of 3a–3d. (i) Six-membered ‘‘[C,N]Pd’’ ring
inversion, (ii) Pd–N(lutidine) bond rotation. The palladated aryl ring is indicated as
C@C for clarity.
The bridge-splitting reaction of five-membered platinacycles of
the type [(C,N)Pt(l-X)]2 with Lewis base, L was shown to afford a
kinetically controlled product trans-[(C,N)PtX(L)] (L = pyridine
[46]) and in some cases trans-[(C,N)PtX(L)] was shown to rearrange
to a thermodynamically controlled cis-[(C,N)PtX(L))] (L = 2,6-luti-
dine and PPh3) upon standing or upon heating [47,48]. Thus, we
suggest that Va and Vb are the kinetic products of the bridge-split-
ting reaction involving II and lutidine [18] whereas 3a, 3c and 3d
are the thermodynamic products of such reaction involving 2a or
2b and lutidine.
[ion]: 929 (90), [MꢀOAc]+; 516 (62), [monomer+Na]+; 464 (50),
[monomerꢀ2 Me]+; 434 (67), [(C,N)Pd]+; 328 (100), [LH2
ꢀH]+.
2-tolyl
Crystals suitable for X-ray diffraction data were grown from
CH2Cl2/toluene mixture at ambient condition over a period of sev-
7
eral days to afford 1aꢁC H8 as shiny greenish yellow crystals.
3. Conclusions
4.2.2. Palladacycle 1b
Palladacycles 1a and 1c were shown to exist as a dimer in the
solid state but as a mixture of predominantly a dimer and a mono-
mer in solution. Palladacycles 2a and 2b were shown to exist as a
dimer in the solid state but as a mixture of a dimer and a trimer in
solution. The presence of two species in solution was ascribed to
the cleavage of OAc/Br bridges in 1a, 1c, 2a, and 2b by solvent mol-
ecule. The stereochemical outcome of the bridge-splitting reaction
was shown to be controlled by steric factor or antisymbiosis. The
number of solution conformers of cis-[(C,N)PdBr(L)] depends not
Yield: 81%. Anal. Calc. for Pd2C48H44N6O4F6ꢁ0.20 CH2Cl2 (Mw:
1112.74): C, 52.03; H, 4.02; N, 7.55. Found: C, 52.05; H, 4.03; N,
7.33%. IR (KBr, cmꢀ1):
(C@N) 1635 vs;
m
(NH) 3424 m, 3378 m;
ma(OCO) 1682 vs;
m
m
s(OCO) 1542 s;
m
(CF3) 1207 vs, 1148 s. 1H NMR
(300 MHz, CDCl3): d 1.75, 1.88, 2.50 (each s, 6 ꢃ 3H, CH3), 5.44 (s,
2H, NH), 6.23 (d, JHH = 7.8 Hz, 2H, ArH), 6.26 (s, 2H, NH), 6.84 (d,
JHH = 6.9 Hz, 2H, ArH), 6.90–6.99 (br, m, 6H, ArH), 7.05 (t,
JHH = 7.5 Hz, 2H, ArH), 7.20, 7.22 (br, 8H, ArH), 7.47 (d, JHH = 7.2 Hz,
2H, ArH). 13C NMR (75.5 MHz, CDCl3): d 17.4, 17.5, 18.9 (CH3),
1
only upon the shape and symmetry but also on the
acceptor characteristics of the Lewis base, L.
r-donor/p-
115.2 (q, JCF = 288.8 Hz, CF3), 118.4, 119.6, 121.1, 125.9, 126.6,
126.7, 127.0, 127.1, 127.5, 128.5, 131.6, 131.8, 133.3, 133.6,
134.1, 134.2, 135.4, 142.2, 144.4 (ArC and C@N), 163.9 (q,
2JCF = 37.5 Hz, OC(O)). 19F NMR (282.4 MHz, CDCl3): d ꢀ74.6.
4. Experimental
4.1. General remarks
4.2.3. Palladacycle 1c
Yield: 88%. Anal. Calc. for Pd2C54H62N6O4 (Mw: 1071.96): C,
60.50; H, 5.83; N, 7.84. Found: C, 60.61; H, 5.82; N, 7.82%. IR
2,4-xylyl
LH22-tolyl, LH2
and PTA were prepared following the re-
ported procedures [19,49]. The instrumental details pertinent to
IR, NMR, mass spectral and microanalytical data are as reported
in our previous publications [18,50]. For few samples, 1H and 13C
(KBr, cmꢀ1):
1592 vs,
(1c): monomer (B) ꢂ 1.00:0.40; d 1.37, 1.66 (s, 2 ꢃ 6H, CH3, 1c),
m
(NH) 3429 m, 3396 m;
m(C@N) 1635 vs; ma(OCO)
m
s(OCO) 1413 s. 1H NMR (400 MHz, CDCl3, 5.0 mM): dimer

K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
1049
1.73 (s, 3H, CH3, B), 1.82 (s, 6H, CH3, 1c), 1.95, 2.15 (each s, 2 ꢃ 3H,
CH3, B), 2.22 (s, 6H, CH3, 1c), 2.23 (s, 3H, CH3, B), 2.29 (s, 6H, CH3,
1c), 2.32, 2.34 (each s, 2 ꢃ 3H, CH3, B), 2.40 (s, 6H, CH3, 1c), 2.49 (br,
6H, CH3, 1c; 3H, CH3, B), 5.27 (s, 2H, NH, 1c), 5.48 (s, 1H, NH, B),
6.00 (s, 2H, NH, 1c), 6.40 (d, JHH = 7.7 Hz, 2H, ArH, 1c), 6.51 (s,
1H, NH, B), 6.66–6.70 (br, 5H, ArH), 6.77 (d, JHH = 8.0 Hz, 2H,
ArH), 6.86 (s, 1H, ArH), 6.93 (d, JHH = 8.1 Hz, 2H, ArH), 6.97 (d,
JHH = 11.7 Hz, 4H, ArH), 7.03–7.20 (br, 6H, ArH), 7.45 (s, 2H, ArH).
13C NMR (75.5 MHz, CDCl3, 90.6 mM): dimer, 1c: d 17.4, 17.5,
19.2, 20.9, 21.1, 23.6, 26.9 (CH3), 118.4, 121.2, 126.3, 126.5,
126.9, 127.2, 127.7, 129.0, 131.9, 132.1, 132.2, 134.1, 134.7,
135.0, 135.2, 137.7, 141.2, 144.0 (ArC and C@N), 179.2 (OC(O)).
Note: Only 18 carbon resonances were observed for ArC and C@N
carbons rather than the expected 19 peaks, presumably due to
Suitable crystals for X-ray diffraction data were grown from
CH2Cl2/toluene mixture at ambient temperature over a period of
several days to afford 2bꢁC7H8 as cuboidal yellow crystals.
4.2.7. Palladacycle 3a
Yield: 88%. Anal. Calc. for PdC29H31N4Br (Mw: 621.91): C, 56.01;
H, 5.02; N, 9.01. Found: C, 55.84; H, 5.20; N, 9.08%. IR (KBr, cmꢀ1):
m
(NH) 3426 m, 3405 m;
CDCl3):
:b conformers ꢂ 3.0:1.0; d 1.57 (s, 3H, CH3, b), 1.69 (s,
3H, CH3, ), 2.10 (s, 3H, CH3, b), 2.13 (s, 3H, CH3, ), 2.26 (s, 3H,
CH3, ), 2.48 (s, 3H, CH3, b), 2.52 (s, 3H, 2,6-(CH3)2C5H3N, b), 2.67
m
(C@N) 1623 vs. 1H NMR (300 MHz,
a
a
a
a
(s, 3H, 2,6-(CH3)2C5H3N,
a), 2.97 (s, 3H, 2,6-(CH3)2C5H3N, b), 3.34
(s, 3H, 2,6-(CH3)2C5H3N,
a
), 5.76 (s, 1H, NH, ), 5.84 (d, JHH = 7.5 Hz,
a
1H, ArH, b), 5.93 (br, 1H, ArH), 6.07 (s, 1H, NH, b), 6.24 (d,
JHH = 7.8 Hz, 1H, ArH, ), 6.30 (br, 1H, NH, b), 6.40 (d, JHH = 7.2 Hz,
1H, ArH, b), 6.45 (s, 1H, NH, ), 6.55–6.74 (m, 5H, ArH), 6.91–7.00
(m, 3H, ArH), 7.14–7.36 (m, 14H, ArH), 7.47–7.54 (m, 1H, ArH),
overlapping peaks. ESI-MS+, m/z (relative intensity %), [ion]: 1013
a
(74), [MꢀOAc]+; 517 (100), [(C,N)Pd+K]+; 370 (91), [LH2
ꢀH]+.
a
2,4-xylyl
Crystals suitable for X-ray diffraction data were grown from tolu-
ene at ambient condition over a period of several days to afford
1c as greenish yellow crystals.
8.00 (d, JHH = 6.6 Hz, 1H, ArH,
a
). ESI-MS+, m/z (relative intensity
%), [ion]: 541 (27), [MꢀBr]+; 475 (100), [(C,N)Pd+K]+; 328 (99),
ꢀH]+.
2-tolyl
[LH2
4.2.4. Palladacycle 1d
Yield: 88%. Anal. Calc. for Pd2C54H56N6O4F6ꢁ0.5C7H8 (Mw:
4.2.8. Palladacycle 3b
1225.97): C, 56.33; H, 4.93; N, 6.85. Found: C, 56.29; H, 5.32; N,
Yield: 85%. Anal. Calc. for PdC29H31N4Brꢁ0.75 C7H8 (Mw:
6.71%. IR (KBr, cmꢀ1):
(C@N) 1635 vs;
m
(NH) 3427 m, 3372 m;
ma(OCO) 1674 vs;
691.02): C, 59.53; H, 5.40; N, 8.11. Found: C, 59.60; H, 5.57; N,
m
m
s(OCO) 1531 s;
m
(CF3) 1205 vs, 1145 s. 1H NMR
8.10%. IR (KBr, cmꢀ1):
m
(NH) 3426 m, 3378 m;
m
(C@N) 1624 vs.
:b conformers ꢂ 3.0:1.5; d 1.65 (s,
a), 2.06 (s, 3H, CH3, b), 2.11 (s, 6H,
(300 MHz, CDCl3): d 1.73, 1.84, 2.21, 2.32, 2.39, 2.46 (each s,
12 ꢃ 3H, CH3), 5.38 (s, 2H, NH), 6.09 (d, JHH = 7.8 Hz, 2H, ArH),
6.20 (s, 2H, NH), 6.69 (t, JHH = 9.0 Hz, 2H, ArH), 6.76 (s, 4H, ArH),
6.95–7.02 (m, 6H, ArH), 7.17 (d, JHH = 7.2 Hz, 2H, ArH). 13C NMR
(75.5 MHz, CDCl3): d 17.3, 17.4, 18.9, 20.8, 20.9, 21.0 (CH3), 115.2
1H NMR (300 MHz, CDCl3):
a
3H, CH3, b), 1.70 (s, 3H, CH3,
3,5-(CH3)2C5H3N, b), 2.18 (s, 3H, CH3, b), 2.22 (s, 6H, 3,5-
(CH3)2C5H3N, ), 5.79 (s, 1H, NH, b),
), 2.36, 2.44 (s, 2 ꢃ 3H, CH3,
6.08 (s, 1H, NH, ), 6.12 (d, JHH = 7.8 Hz, 1H, ArH, ), 6.44 (s, 1H,
NH, ), 6.49 (t, JHH = 7.5 Hz, 2H, ArH, ), 6.67–6.80 (m, 2H, ArH;
1H, NH, b), 6.94 (t, JHH = 7.5 Hz, 1H, ArH, b), 7.06–7.40 (m, 15H,
ArH), 7.46 (d, JHH = 7.5 Hz, 1H, ArH, ), 7.81 (s, 1H, 4-H, 3,5-
Me2C5H3N, ), 8.09 (dd, JHH = 9.0; 3.0 Hz, 1H, 4-H, 3,5-Me2C5H3N,
a
a
a
a
1
(q, JCF = 288.2 Hz, CF3), 118.1, 119.2, 126.0, 126.9, 127.1, 127.7,
a
a
127.9, 129.8, 131.0, 131.6, 132.0, 132.3, 133.8, 134.0, 135.2,
2
136.2, 138.4, 139.7, 144.4 (ArC and C@N), 163.5 (q, JCF = 37.8 Hz,
a
OC(O)). 19F NMR (282.4 MHz, CDCl3): d ꢀ74.8.
a
b), 8.24 (br, 2H, 2-H, 3,5-Me2C5H3N, b), 8.42 (s, 1H, 2-H, 3,5-
4.2.5. Palladacycle 2a
Me2C5H3N,
a
), 8.49 (s, 1H, 2-H, 3,5-Me2C5H3N, b). ESI-MS+, m/z (rel-
ative intensity %), [ion]: 475 (94), [(C,N)Pd+K]+; 328 (100), [LH2
2-
Yield: 87%. Anal. Calc. for Pd2C44H44N6Br2ꢁ2.5CHCl3 (Mw:
ꢀH]+.
tolyl
1327.97): C, 42.06; H, 3.53; N, 6.33. Found: C, 41.68/41.88; H,
3.49/3.36; N, 6.26/6.28%. IR (KBr, cmꢀ1):
m
(NH) 3422 m, 3385 m;
m
(C@N) 1625 vs. 1H NMR (400 MHz, CD2Cl2): d 1.63, 2.07, 2.34
4.2.9. Palladacycle 3c
(each s, 3 ꢃ 3H, CH3), 5.94 (br), 5.99 (br), 6.34 (br), 6.55 (t,
JHH = 7.2 Hz), 6.69 (d, JHH = 7.2 Hz), 7.11–7.33 (br m) (ArH and
NH). The 13C NMR spectrum for 2a was not recorded owing to its
poor solubility in common deuterated solvents. ESI-MS+, m/z (rela-
Yield: 88%. Anal. Calc. for PdC29H31N4Br (Mw: 621.91): C, 56.01;
H, 5.02; N, 9.01. Found: C, 56.03/56.04; H, 5.28/5.17; N, 8.99/9.01%.
IR (KBr, cmꢀ1):
(300 MHz, CDCl3):
(br s, 12H, CH3, a a
, b, a0, b0), 2.11 (br s, 12H, CH3, , b, a0, b0), 2.18
m(NH) 3418 m, 3314 m; m
(C@N) 1623 vs. 1H NMR
a
:b: a0:b0 conformers ꢂ 3.0:2.3:0.5:0.5; d 1.69
tive intensity %), [ion]: 1464 (100), [CꢀBr]+; 949 (28), [2aꢀBr]+;
475 (30), [(C,N)Pd+K]+; 328 (95) [LH2
ꢀH]+. Suitable crystals
(s, 3H, CH3, a0), 2.23 (s, 3H, CH3, b0), 2.26 (s, 3H, 2,4-(CH3)2C5H3N,
a0), 2.31 (s, 6H, CH3, , b), 2.42 (s, 3H, 2,4-(CH3)2C5H3N, b0), 2.46
(s, 3H, 2,4-(CH3)2C5H3N, b), 2.48 (s, 3H, 2,4-(CH3)2C5H3N, ), 2.54
(s, 3H, 2,4-(CH3)2C5H3N, a0), 2.79 (s, 3H, 2,4-(CH3)2C5H3N, b), 3.06
(s, 3H, 2,4-(CH3)2C5H3N, b0), 3.16 (s, 3H, 2,4-(CH3)2C5H3N,
), 5.73,
2-tolyl
for X-ray diffraction study were grown from CHCl3 at ambient tem-
perature over a period of several days to afford 2aꢁ3CHCl3 as cuboi-
dal yellow crystals.
a
a
a
4.2.6. Palladacycle 2b
5.86, 6.00 (t, JHH = 6.3 Hz), 6.08 (d, JHH = 5.1 Hz), 6.44, 6.48, 6.51,
6.63, 6.70, 6.71, 6.73 (br), 6.82–6.99 (m), 7.12, 7.17 (d, JHH = 7.2 Hz),
7.29, 7.47 (d, JHH = 7.8 Hz), 7.80 (d, JHH = 6.0 Hz), 8.10 (m), 8.49 (d,
JHH = 5.7 Hz), 8.85 (d, JHH = 5.4 Hz) (ArH and NH).
Yield: 85%. Anal. Calc. for Pd2C50H56N6Br2ꢁ2.5 CH2Cl2 (Mw:
1326.03): C, 47.55; H, 4.64; N, 6.34. Found: C, 47.76; H, 4.66; N,
6.55%. IR (KBr, cmꢀ1):
m(NH) 3409 m, 3386 m; m(C@N) 1626 vs.
1H NMR (300 MHz, CDCl3): d 1.60, 2.03, 2.15 (each s, 6 ꢃ 3H,
CH3), 2.23, 2.27, 2.31 (each br, 6 ꢃ 3H, CH3), 5.79, 5.85 (br, 2H,
ArH), 6.21, 6.48 (each s, 2 ꢃ 2H, NH), 6.95–7.17 (br m, 14H, ArH).
13C NMR (100.81 MHz, CDCl3): d 16.9, 17.7, 19.1, 20.7, 21.1 (CH3),
120.3, 120.5, 123.8, 124.0, 124.4, 126.8, 126.9 (CH), 127.3 (CH),
128.4 (CH), 130.6, 130.8 (br), 131.4, 131.8 (CH), 131.9 (CH), 132.1
(CH), 132.3 (CH), 133.9, 134.3 (br), 135.3, 135.6, 136.0, 138.2
(CH), 138.7, 141.3, 141.5, 141.8, 146.7 (ArC and C@N). Note: Only
five carbon resonances were observed for CH3 carbons rather than
the expected six peaks due to overlap at d = 21.1 ppm. ESI-MS+, m/z
4.2.10. Palladacycle 3d
Yield: 93%. Anal. Calc. for PdC32H37N4Br (Mw: 663.99): C, 57.88;
H, 5.62; N, 8.44. Found: C, 58.13; H, 5.41; N, 8.60%. IR (KBr, cmꢀ1):
m
(NH) 3412 m, 3300 w;
CDCl3):
:b conformers ꢂ 3.0:0.6; d 1.66, 1.89, 2.04 (each s,
3 ꢃ 3H, CH3, ), 2.07, 2.16, 2.20, 2.23 (each s, 4 ꢃ 3H, CH3, b),
2.30 (br s, 6H, CH3, ), 2.52
, b), 2.33, 2.41 (each s, 2 ꢃ 3H, CH3,
(s, 3H, CH3, b), 2.67 (s, 3H, 2,6-(CH3)2C5H3N, b), 2.97 (s, 3H, 2,6-
m
(C@N) 1626 vs. 1H NMR (400 MHz,
a
a
a
a
(CH3)2C5H3N,
(CH3)2C5H3N,
a
a
), 3.32 (s, 3H, 2,6-(CH3)2C5H3N, b), 3.33 (s, 3H, 2,6-
), 5.58 (s, 1H, NH, ), 5.66 (s, 1H, NH, b), 5.98 (s,
(relative intensity %), [ion]: 1592 (33), [DꢀBr]+; 1122 (48),
a
[2b+Li]+; 519 (39), [(C,N)Pd+K]+, 370 (100) [LH2
ꢀH]+.
1H, NH, a), 6.08 (d, JHH = 8.2, 1H, ArH, b), 6.33 (s, 1H, NH, b), 6.35
2,4-xylyl

1050
K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
(s, 1H, ArH,
a
), 6.50 (s, 1H, ArH,
a
), 6.52 (s, 1H, ArH, b), 6.63
temperature for 24 h. The solution was concentrated under vac-
uum to about 5 mL, layered with MeOH and stored at ambient
temperature for several days to afford 5ꢁ2CH3OH as yellow cuboi-
dal crystals. Yield: 83% (118 mg, 0.160 mmol). Anal. Calc. for
PdC28H34N6PBrꢁ2CH3OH (Mw: 735.99): C, 48.96; H, 5.75; N,
(d, JHH = 7.4, 1H, ArH, b), 6.97, 6.99 (each s, 2H, ArH), 7.02 (s, 2H,
ArH), 7.04 (s, 2H, ArH), 7.07, 7.08 (br m, 3H, ArH), 7.13
(d, JHH = 7.3, 1H, ArH), 7.34 (s, 3H, ArH), 7.36 (s, 2H, ArH), 7.50
(t, JHH = 7.6, 1H, ArH), 7.81 (s, 1H, ArH). TOF MS+, m/z (relative
intensity %), [ion]: 583 (100), [MꢀBr]+; 477 (33), [MꢀBr,L]+; 370
11.42. Found: C, 48.82; H, 6.00; N, 11.62%. IR (KBr, cmꢀ1):
m
(NH)
(33) [LH2
ꢀH]+. Suitable crystals for X-ray diffraction data
3414 m, 3361 w; m
(C@N) 1614 vs. 1H NMR (400 MHz, CDCl3): d
2,4-xylyl
were grown from CH2Cl2/n-hexane mixture at ambient tempera-
ture over a period of several days to afford 3d as yellow crystals.
1.64, 2.05, 2.12 (each s, 3 ꢃ 3H, CH3), 4.28, 4.45 (each s, 6 ꢃ 2H,
CH2), 6.08, 6.27 (each s, 2 ꢃ 1H, NH), 6.75–6.80 (m, 2H, ArH),
7.08–7.12 (m, 2H, ArH), 7.16–7.18 (m, 1H, ArH), 7.23 (d, JHH = 7.5,
1H, ArH), 7.27 (s, 1H, ArH), 7.28–7.30 (m, 3H, ArH), 7.35 (d,
JHH = 6.8, 1H, ArH). 13C NMR (100.81 MHz, CDCl3): d 16.9, 17.8,
19.1 (CH3), 53.2 (d, JCP = 17.3 Hz, PCH2), 73.2 (d, JCP = 6.7 Hz,
NCH2), 122.8 (d, JCP = 4.8 Hz), 123.3, 123.4, 126.1 (d, JCP = 8.6 Hz),
126.6, 127.8, 128.1, 129.1 (d, JCP = 19.2 Hz), 131.2, 131.8, 131.9,
133.4, 134.6, 134.7, 136.2, 136.6, 137.6 (d, JCP = 14.4 Hz), 143.8,
148.4 (ArC and C@N). 13P NMR (CDCl3, 161.8 MHz): d ꢀ48.8. TOF
MS+, m/z (relative intensity %), [ion]: 673 (15), [M+H]+; 629 (30),
4.2.11. Palladacycle 4
To a suspension of 2a (200 mg, 0.194 mmol) in CH2Cl2 (10 mL)
was added a solution of tBuN„C (34 mg, 0.41 mmol) made in
CH2Cl2 (5 mL). The resulting mixture was stirred at room temper-
ature for 2 h. During the course of the reaction the solid dissolved
to afford a clear solution. The solution was concentrated under vac-
uum to about 5 mL and layered with n-hexane to afford 4 as green
crystals after several days. Yield: 88% (205 mg, 0.343 mmol). Mp:
159 °C (dec.). Anal. Calc. for PdC27H31N4Br (Mw: 597.89): C,
54.24; H, 5.22; N, 9.37. Found: C, 54.03; H, 5.27; N, 9.43%. IR
[M+2Hꢀ3Me]+; 591 (100), [MꢀBr]+; 458 (10), [MꢀPTA, Br+Na]+,
2-tolyl
328 (72) [LH2
ꢀH]+. Suitable crystals for X-ray diffraction
study were grown from CH3OH at ambient temperature over a per-
(KBr, cmꢀ1):
m(NH) 3418 m, 3326 w; m(C„N) 2215 vs; m(C@N)
iod of several days to afford 5ꢁCH3OH as irregular yellow crystals.
1621 vs. 1H NMR (400 MHz, CDCl3): d 1.50 (s, 9H, CH3), 1.67,
2.11, 2.34 (each s, 3 ꢃ 3H, CH3), 6.01, 6.38 (each s, 2 ꢃ 1H, NH),
6.72 (t, JHH = 7.3, 1H, ArH), 6.82 (d, JHH = 7.3, 1H, ArH), 7.12–7.16
(m, 2H, ArH), 7.28–7.34 (m, 7H, ArH). 13C NMR (100.81 MHz,
CDCl3): d 17.2, 17.7, 19.1, 30.0 (CH3), 57.7 (Me3CN„C), 122.2
(CH), 122.6, 126.3 (CH), 127.0 (CH), 127.8 (CH), 128.1 (CH), 128.2
(Me3CN„C), 128.7 (CH), 129.0 (CH), 131.0 (CH), 131.6, 131.8
(CH), 134.1, 134.3, 134.8, 136.5, 139.4 (CH), 144.0, 146.7 (ArC and
C@N). Note: Only 18 carbon resonances were observed for ArC
and C@N carbons rather than the expected 19 peaks, due to two
overlapping peaks at d = 126.3 ppm. TOF MS+, m/z (relative inten-
sity %), [ion]: 583 (100), [MꢀMe]+.
4.2.13. Palladacycle 6
Yield: 93%. Anal. Calc. for PdC40H40N5Br (Mw: 777.11): C, 61.82;
H, 5.19; N, 9.01. Found: C, 62.18; H, 5.19; N, 8.89%. IR (KBr, cmꢀ1):
m(NH) 3382 m; m(C„N) 2177 vs; m(C@NXy) 1628 s; m(C@N) 1568
vs. 1H NMR (300 MHz, CDCl3): d 2.06 (br, 6H, 2,6-(CH3)2C6H3N„C),
2.16 (s, 6H, 2,6-(CH3)2C6H3N„C), 2.31 (s, 3H, CH3), 2.43, 2.76 (each
br, 2 ꢃ 3H, CH3), 5.92 (br, 1H, NH), 6.49 (br, 1H, ArH), 6.53 (t,
JHH = 7.2 Hz, 1H, ArH), 6.92–7.28 (br m, 14H, ArH), 7.69 (d,
JHH = 7.2 Hz, 1H, ArH), 9.84 (br, 1H, NH). 13C NMR (75.47 MHz,
CDCl3): d 17.9 (br, CH3), 18.3, 18.6, 20.0 (br, CH3), 121.9 (br),
122.9 (br), 123.4 (br), 124.7 (br), 125.2 (br), 126.0, 126.7, 127.3,
128.2 (br), 128.8, 129.0, 129.2, 130.6, 132.9, 134.6, 134.8 (br),
141.0 (br), 142.9 (br), 149.8 (ArC), 151.6 (Pd–C„N), 154.2 (Pd–
N@C), 177.2 (Pd–C@N). Note: Only four carbon resonances were
observed for CH3 carbon rather than the expected five peaks and
4.2.12. Palladacycle 5
A solution of PTA (30 mg, 0.19 mmol) in CH2Cl2 (10 mL) was
added to the suspension of 2a (100 mg, 0.097 mmol) in CH2Cl2
(10 mL) and the resulting mixture was stirred at ambient
Table 8
Crystallographic and refinement data for 1aꢁC7H8, 1c, 2aꢁ3CHCl3, 2bꢁC7H8 and 3a.
1aꢁC7H8
1c
2aꢁ3CHCl3
2bꢁC7H8
3a
Formula
Fw
T (K)
Pd2C55H58N6O4
1079.87
298(2)
Pd2C54H62N6O4
1071.90
298(2)
Pd2C47H47N6Br2Cl8
1387.58
298(2)
Pd2C57H64N6Br2
1205.76
298(2)
PdC29H31N4Br
621.89
100(2)
k (Å)
0.71073
monoclinic
C2/c
15.225(3)
17.592(3)
19.150(5)
90.00
104.281(3)
90.00
4970.7(17)
4
0.71073
0.71073
monoclinic
C2/c
0.71073
0.71073
triclinic
P1
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
12.297(7)
17.823(11)
25.043(15)
78.499(13)
75.943(12)
79.822(12)
5169(5)
4
22.684(2)
18.244(1)
14.705(1)
90.00
116.011(11)
90.00
5469.3(8)
4
1.685
13.0583(5)
14.5003(6)
17.1901(8)
113.085(4)
95.030(3)
110.903(4)
2697.4(3)
2
11.4763(6)
12.3050(6)
12.3960(7)
93.515(2)
116.767(3)
115.592(2)
1336.56(14)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ3
F(000)
)
1.443
2216
0.775
1.377
2208
0.745
1.485
1220
2.190
1.545
628
2.213
2744
2.597
l
(mmꢀ1
)
h range (°)
1.80–27.00
5458
4433
1.56–26.37
21048
11924
2.84–26.37
5584
4807
2.89–26.37
11016
8634
1.94–35.49
12063
10324
Reflections measured
Reflections used
Parameters
308
1229
296
612
322
R[I > 2
R1
r(I)]
0.0343
0.0662
0.0554
0.0405
0.0311
wR2
0.0964
1.051
0.716/ꢀ0.675
0.1001
1.021
0.696/ꢀ0.451
0.1644
1.034
1.098/ꢀ1.200
0.0983
1.054
0.705/ꢀ0.550
0.0864
1.154
1.406/ꢀ1.158
Goodness of fit on F2
Largest difference in peak/hole (e Åꢀ3
)

K. Gopi et al. / Polyhedron 52 (2013) 1041–1052
1051
Table 9
Crystallographic and refinement data for 3c, 3d, 4, 5ꢁCH3OH and 6.
Complex
3c
3d
4
5ꢁCH3OH
6
Formula
Fw
PdC29H31N4Br
621.89
PdC32H37N4Br
663.97
PdC27H31N4Br
597.87
PdC29H38N6OBrP
703.93
PdC40H40N5Br
777.08
T (K)
298(2)
100(2)
100(2)
100(2)
298(2)
k (Å)
0.71073
0.71073
0.71073
0.71073
monoclinic
P21/c
0.71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
11.4400(5)
11.6168(6)
12.7373(6)
83.097(2)
66.736(2)
62.235(2)
1371.82(11)
2
12.313(3)
12.510(3)
12.585(3)
67.563(3)
62.364(3)
70.746(4)
1559.5(6)
2
11.6871(4)
11.8770(5)
11.9081(6)
109.233(4)
116.846(4)
99.067(3)
1297.14(13)
2
10.613(5)
12.422(5)
22.387(5)
90.000(5)
91.834(5)
90.000(5)
2949.9(19)
4
10.7869(2)
12.8400(3)
14.0246(3)
99.3450(10)
100.9230(10)
104.8270(10)
1797.69(7)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ3
F(000)
)
1.506
628
2.156
1.414
676
1.902
1.531
604
2.277
1.585
1432
2.072
1.436
792
1.662
l
(mmꢀ1
)
h range (°)
1.75–30.03
7942
3977
1.90–27.70
7356
4965
2.97–26.37
5305
4305
1.82–27.00
6437
5274
1.52–29.13
9559
7210
Reflections measured
Reflections used
Parameters
319
356
304
353
431
R[I > 2
R1
r(I)]
0.0484
0.0737
0.0350
0.0469
0.0369
wR2
0.0922
0.957
0.609/ꢀ0.437
0.1728
1.131
1.630/ꢀ2.304
0.0973
1.029
0.792/ꢀ1.289
0.1350
1.248
2.561/ꢀ1.608
0.0868
1.010
1.098/ꢀ1.200
Goodness of fit on F2
Largest difference in peak/hole (e Aꢀ3
)
19 carbon resonances were observed for ArC rather than the ex-
pected 26 peaks presumably due to overlapping peaks. ESI-MS+,
m/z (relative intensity %), [ion]: 778 (100), [M+H]+; 732 (45),
[Mꢀ3Me]+; 696 (83), [MꢀBr]+; 565 (40) [(C,N)Pd+H]+. Crystals suit-
able for X-ray diffraction data were grown from CH2Cl2/toluene
mixture at ambient condition over a period of several hours.
Appendix A. Supplementary data
CCDC 859650–859659 contain the supplementary crystallo-
graphic data for 1aꢁC7H8, 1c, 2aꢁ3CHCI3, 2bꢁC7H8, 3a, 3c, 3d, 4,
5ꢁCH3OH and 6. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2012.06.077.
4.3. Crystal structure determinations
Suitable crystals of 1aꢁC7H8, 1c, 2aꢁ3CHCl3, 2bꢁC7H8, 3a, 3c, 3d,
4, 5ꢁCH3OH and 6 for X-ray diffraction study were carefully se-
lected after examination under an optical microscope and mounted
on the goniometer head with a paraffin oil coating. The unit cell
parameters and intensity data for 1aꢁC7H8, 1c, 3c and 6 were col-
lected at 298 K and those of 3a, 3d, 4 and 5ꢁCH3OH were collected
at 100 K using a Bruker SMART APEX CCD diffractometer equipped
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